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Issue 24, 2012
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Temperature and solvent structure dependence of VO2+ complexes of pyridine-N-oxide derivatives and their interaction with human serum transferrin

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Abstract

The behaviour of the systems formed by VO2+, 2-hydroxypyridine-N-oxide (Hhpo) and 2-mercaptopyridine-N-oxide (Hmpo) was studied both in solution and in the solid state through the combined application of spectroscopic (EPR and UV-Vis spectroscopy) and DFT methods. The geometry of solid bis-chelated complexes [VOL2], with L = hpo and mpo, is square pyramidal, but it can change to cis-[VOL2S], where S is a solvent molecule, when these are dissolved in a coordinating solvent. The equilibrium between the square pyramidal and cis-octahedral forms is strongly affected by solvent and temperature. At room temperature, the predominant species is [VOL2], which gives a pink colour to the solutions; at lower temperatures, the equilibrium is shifted—partially or completely—toward the formation of cis-[VOL2S], which is green. In an acidic environment and in the presence of an excess of ligand, [VOL2] can transform into the tris-chelated complex [VL3]+, in which vanadium loses the oxido ligand and adopts a hexa-coordinated geometry intermediate between octahedral and trigonal prismatic. 1-Methylimidazole (1-MeIm), which represents a model for His–N coordination, forms mixed complexes with stoichiometry cis-[VOL2(1-MeIm)], occupying an equatorial position. In the ternary systems VO2+–Hhpo–hTf and VO2+–Hmpo–hTf at room temperature and pH 7.4, besides (VO)hTf and (VO)2hTf, the mixed species cis-VO(hpo)2(hTf) and VO(mpo)(hTf) are observed, with the equatorial binding of an accessible histidine residue. Finally, the contribution of the N-oxide group to 51V Az and Aiso hyperfine coupling constants, which can be important in the characterisation of similar species, is discussed.

Graphical abstract: Temperature and solvent structure dependence of VO2+ complexes of pyridine-N-oxide derivatives and their interaction with human serum transferrin

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Publication details

The article was received on 29 Dec 2011, accepted on 30 Mar 2012 and first published on 30 Mar 2012


Article type: Paper
DOI: 10.1039/C2DT12503J
Citation: Dalton Trans., 2012,41, 7304-7318

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    Temperature and solvent structure dependence of VO2+ complexes of pyridine-N-oxide derivatives and their interaction with human serum transferrin

    D. Sanna, V. Ugone, G. Micera and E. Garribba, Dalton Trans., 2012, 41, 7304
    DOI: 10.1039/C2DT12503J

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